When video is streamed over the Internet and played back through a Web browser or media player, the video is delivered in digital form. Digital video is also used when video is delivered through many broadcast services, satellite services and cable television services. Real-time videoconferencing often uses digital video, and digital video is used during video capture with most smartphones, Web cameras and other video capture devices. Digital video is also used for technologies such as virtual reality and augmented reality, whether video is played back in a head-mounted display, mobile device, or other type of device.
Panoramic video is video in which views in multiple directions around a central position are recorded at the same time. The recorded video can include image content in every direction, or at least image content in every direction in a 360-degree sphere around the central position, including at least some image content above the central position and at least some image content underneath the central position. Panoramic video is sometimes called 360-degree video, immersive video, or spherical video. Panoramic video can be captured using an omnidirectional camera or a collection of multiple cameras pointing in different directions. For modern-day applications, panoramic video is processed in digital form during stages of creation, editing, and delivery, as well as stages of reconstruction and rendering for playback.
During playback, a viewer typically can control a view direction relative to the central position, potentially changing which section of the panoramic video is viewed over time. In some systems, a viewer can also zoom in or zoom out, which effectively changes the field of view of the panoramic video. When panoramic video is rendered for display, the section of the panoramic video that is viewed may be projected to a flat image, which is called a screen projection. For a mobile device or computer monitor, a single screen projection may be rendered. For a head-mounted display (or mobile device held in a head-mounted band), the section of the panoramic video that is viewed may be projected to two screen projections, for the left and right eyes, respectively.
When a computer system reconstructs and renders panoramic video, resources may be wasted reconstructing image content that is not viewed. For example, memory may be used to store sample values for areas of the panoramic video that are not viewed, and processing cycles may be used to determine the non-viewed sample values and their locations at different stages of processing.